1. Field of the Invention
This invention relates to a coating composition having a binder of epoxy resin and polysiloxane precondensate that is useful as a release finish for cooking vessels because of its thermal stability, release properties, hardness, glossy appearance and abrasion resistance. Particularly, this invention relates to a coating composition useful for coating tin-plated steel cooking vessels because it is curable at a temperature which is lower than the melting point of tin, about 232.degree. C.
2. Prior Art
Cookware and bakeware items have been coated with fluorocarbon polymers, such as polytetrafluoroethylene and copolymers thereof. Finishes of polytetrafluoroethylene have excellent thermal stability and good release properties and have been widely used and well accepted. However, a primer is generally required for these coatings, along with special treatment of the metal substrate, to obtain excellent adhesion of the coating. Additionally, since the temperature needed to fuse the fluorocarbon polymer is higher than the melting point of tin, it cannot be used upon tin-plated metals. Therefore, it would be desirable to have a coating composition that could be applied to unprimed metal substrates, including tin, and would form a finish that has release properties and also good abrasion and scratch resistance.
The novel coating composition of this invention can be applied directly to metal without the use of a primer, forms a finish that has release properties, outstanding adhesion to unprimed metal, thermal stability, good hardness, abrasion resistance, and glossy appearance and is an ideal coating composition for cooking vessels, particularly tin-plated ones.
U.S. Pat. No. 3,170,962--Tyler discloses coating compositions of epoxy and polysiloxane resins. While the examples of Tyler indicate they use polysiloxanes having 3 or 4% silanol, this is before the copolymerization with epoxies. During the copolymerization, at least a substantial proportion of these silanol groups would be consumed, so that the copolymer would have far less than 4% silanol. If one attempted to make a coating composition of Tyler's copolymer, it would have a relatively low silanol content, substantially below 4%. U.S. Pat. No. 3,801,522--Vasta and U.S. Pat. No. 3,925,276--Merrill teach polysiloxane coatings which do not include epoxy resin.